UPSMON(8) Network UPS Tools (NUT) UPSMON(8)
upsmon - UPS monitor and shutdown controller
upsmon -c command
upsmon [-d] [-i] [-p] [-u user]
upsmon is the client process that is responsible for the most important part of UPS moni-
toring - shutting down the system when the power goes out. It can call out to other
helper programs for notification purposes during power events.
upsmon can monitor multiple systems using a single process. Every UPS that is defined in
the upsmon.conf(5) configuration file is assigned a power value and a type (slave or mas-
-h Display the help message.
Send the command command to the existing upsmon process. Valid commands are:
fsd - shutdown all master UPSes (use with caution)
stop - stop monitoring and exit
reload - reread upsmon.conf(5) configuration file. See "reloading nuances" below
if this doesn't work.
-d Enable debugging mode. upsmon runs in the foreground and prints debugging informa-
tion on stdout about the monitoring process.
-i Enable infinite loop at shutdown. upsmon will keep a process running after calling
the shutdown command rather than exiting. This is only useful if you have shutdown
scripts that complain when upsmon isn't running as they kill various processes.
-p Run privileged all the time. Normally upsmon will split into two processes. The
majority of the code runs as an unprivileged user, and only a tiny stub runs as
root. This switch will disable that mode, and run the old "all root all the time"
Set the user for the unprivileged monitoring process. This has no effect when
The default user is set at configure time with 'configure --with-user=...'. Typi-
cally this is 'nobody', but other distributions will probably have a specific 'nut'
user for this task. If your notification scripts need to run as a specific user,
set it here.
You can also set this in the upsmon.conf(5) file with the RUN_AS_USER directive.
In the upsmon.conf(5), you must specify at least one UPS that will be monitored. Use the
MONITOR system powervalue username password type
The system refers to a upsd(8) server, in the form [<upsname>@]hostname[:port]. The sim-
plest form is just a hostname, i.e.:
"localhost" refers to the first UPS on the local system.
Other possibilities include:
"su700@mybox" means a UPS called "su700" on a system called "mybox".
"elvis:1234" means the first UPS on a system called "elvis", port 1234.
Finally, to use all of these options:
"fenton@bigbox:5678" is a UPS called "fenton" on a system called "bigbox" which runs
upsd(8) on port "5678". Phew!
The powervalue refers to how many power supplies on this system are being driven this UPS.
This is typically set to 1, but see the section on power values below.
The username is a section in your upsd.users(5) file. Whatever password you set in that
section must match the password set in this file.
The type set in that section must also match the type here - master or slave. In general,
a master process is one running on the system with the UPS actually plugged into a serial
port, and a slave is drawing power from the UPS but can't talk to it directly. See the
section on UPS types for more.
upsmon senses several events as it monitors each UPS. They are called notify events as
they can be used to tell the users and admins about the change in status. See the addi-
tional NOTIFY-related sections below for information on customizing the delivery of these
ONLINE The UPS is back on line.
ONBATT The UPS is on battery.
The UPS battery is low (as determined by the driver).
FSD The UPS has been commanded into the "forced shutdown" mode.
COMMOK Communication with the UPS has been established.
Communication with the UPS was just lost.
The local system is being shut down.
The UPS needs to have its battery replaced.
NOCOMM The UPS can't be contacted for monitoring.
In upsmon.conf(5), you can configure a program called the NOTIFYCMD that will handle
events that occur.
NOTIFYCMD "path to program"
Remember to wrap the path in "quotes" if it contains any spaces.
The program you run as your NOTIFYCMD can use the environment variables NOTIFYTYPE and
UPSNAME to know what has happened and on which UPS. It also receives the notification
message (see below) as the first (and only) argument, so you can deliver a preformatted
Note that the NOTIFYCMD will only be called for a given event when you set the EXEC flag
by using the notify flags, below:
By default, all notify events (see above) generate a global message (wall) to all users,
plus they are logged via the syslog. You can change this with the NOTIFYFLAG directive in
the configuration file:
NOTIFYFLAG notifytype flags
NOTIFYFLAG ONLINE SYSLOG
NOTIFYFLAG ONBATT SYSLOG+WALL
NOTIFYFLAG LOWBATT SYSLOG+WALL+EXEC
The flags that can be set on a given notify event are:
SYSLOG Write this message to the syslog.
WALL Send this message to all users on the system via 'wall'.
EXEC Execute the NOTIFYCMD.
IGNORE Don't do anything. If you use this, don't use any of the other flags.
You can mix these flags. "SYSLOG+WALL+EXEC" does all three for a given event.
upsmon comes with default messages for each of the NOTIFY events. These can be changed
with the NOTIFYMSG directive.
NOTIFYMSG type "message"
NOTIFYMSG ONLINE "UPS %s is getting line power"
NOTIFYMSG ONBATT "Someone pulled the plug on %s"
The first instance of %s is replaced with the identifier of the UPS that generated the
event. These messages are used when sending walls to the users directly from upsmon, and
are also passed to the NOTIFYCMD.
The "current overall power value" is the sum of all UPSes that are currently able to sup-
ply power to the system hosting upsmon. Any UPS that is either on line or just on battery
contributes to this number. If a UPS is critical (on battery and low battery) or has been
put into "forced shutdown" mode, it no longer contributes.
A "power value" on a MONITOR line in the config file is the number of power supplies that
the UPS runs on the current system.
MONITOR upsname powervalue username password type
Normally, you only have one power supply, so it will be set to 1.
MONITOR myups@myhost 1 username mypassword master
On a large server with redundant power supplies, the power value for a UPS may be greater
than 1. You may also have more than one of them defined.
MONITOR ups-alpha@myhost 2 username mypassword master
MONITOR ups-beta@myhost 2 username mypassword master
You can also set the power value for a UPS to 0 if it does not supply any power to that
system. This is generally used when you want to use the upsmon notification features for
a UPS even though it's not actually running the system that hosts upsmon. Don't set this
to "master" unless you really want to power this UPS off when this instance of upsmon
needs to shut down for its own reasons.
MONITOR faraway@anotherbox 0 username mypassword slave
The "minimum power value" is the number of power supplies that must be receiving power in
order to keep the computer running.
Typical PCs only have 1, so most users will leave this at the default.
If you have a server or similar system with redundant power, then this value will usually
be set higher. One that requires three power supplies to be running at all times would
simply set it to 3.
When the current overall power value drops below the minimum power value, upsmon starts
the shutdown sequence. This design allows you to lose some of your power supplies in a
redundant power environment without bringing down the entire system while still working
properly for smaller systems.
upsmon and upsd(8) don't always run on the same system. When they do, any UPSes that are
directly attached to the upsmon host should be monitored in "master" mode. This makes
upsmon take charge of that equipment, and it will wait for slaves to disconnect before
shutting down the local system. This allows the distant systems (monitoring over the net-
work) to shut down cleanly before upsdrvctl shutdown runs and turns them all off.
When upsmon runs as a slave, it is relying on the distant system to tell it about the
state of the UPS. When that UPS goes critical (on battery and low battery), it immedi-
ately invokes the local shutdown command. This needs to happen quickly. Once it discon-
nects from the distant upsd(8) server, the master upsmon will start its own shutdown
process. Your slaves must all shut down before the master turns off the power or filesys-
tem damage may result.
upsmon deals with slaves that get wedged, hang, or otherwise fail to disconnect from
upsd(8) in a timely manner with the HOSTSYNC timer. During a shutdown situation, the mas-
ter upsmon will give up after this interval and it will shut down anyway. This keeps the
master from sitting there forever (which would endanger that host) if a slave should break
somehow. This defaults to 15 seconds.
If your master system is shutting down too quickly, set the FINALDELAY interval to some-
thing greater than the default 15 seconds. Don't set this too high, or your UPS battery
may run out of power before the master upsmon process shuts down that system.
For those rare situations where the shutdown process can't be completed between the time
that low battery is signalled and the UPS actually powers off the load, use the upss-
ched(8) helper program. You can use it along with upsmon to schedule a shutdown based on
the "on battery" event. upssched can then come back to upsmon to initiate the shutdown
once it's run on battery too long.
This can be complicated and messy, so stick to the default critical UPS handling if you
REDUNDANT POWER SUPPLIES
If you have more than one power supply for redundant power, you may also have more than
one UPS feeding your computer. upsmon can handle this. Be sure to set the UPS power val-
ues appropriately and the MINSUPPLIES value high enough so that it keeps running until it
really does need to shut down.
For example, the HP NetServer LH4 by default has 3 power supplies installed, with one bay
empty. It has two power cords, one per side of the box. This means that one power cord
powers two power supply bays, and that you can only have two UPSes supplying power.
Connect UPS "alpha" to the cord feeding two power supplies, and UPS "beta" to the cord
that feeds the third and the empty slot. Define alpha as a powervalue of 2, and beta as a
powervalue of 1. Set the MINSUPPLIES to 2.
When alpha goes on battery, your current overall power value will stay at 3, as it's still
supplying power. However, once it goes critical (on battery and low battery), it will
stop contributing to the current overall power value. That means the value will be 1
(beta alone), which is less than 2. That is insufficient to run the system, and upsmon
will invoke the shutdown sequence.
However, if beta goes critical, subtracting its contribution will take the current overall
value from 3 to 2. This is just high enough to satisfy the minimum, so the system will
continue running as before. If beta returns later, it will be re-added and the current
value will go back to 3. This allows you to swap out UPSes, change a power configuration,
or whatever, as long as you maintain the minimum power value at all times.
Besides being able to monitor multiple UPSes, upsmon can also monitor them as different
roles. If you have a system with multiple power supplies serviced by separate UPS batter-
ies, it's possible to be a master on one and a slave on the other. This usually happens
when you run out of serial ports and need to do the monitoring through another system
This is also complicated, especially when it comes time to power down a UPS that has gone
critical but doesn't supply the local system. You can do this with some scripting magic
in your notify command script, but it's beyond the scope of this manual.
When upsmon is forced to bring down the local system, it sets the "FSD" (forced shutdown)
flag on any UPSes that it is running in master mode. This is used to synchronize slaves
in the event that a master UPS that is otherwise OK needs to be brought down due to some
pressing event on the master.
You can manually invoke this mode on the master upsmon by starting another copy with '-c
fsd'. This is useful when you want to initiate a shutdown before the critical stage
through some external means, such as upssched(8).
In the event that upsmon can't reach upsd(8), it declares that UPS "dead" after some
interval controlled by DEADTIME in the upsmon.conf(5). If this happens while that UPS was
last known to be on battery, it is assumed to have gone critical and no longer contributes
to the overall power value.
upsmon will alert you to a UPS that can't be contacted for monitoring with a "NOCOMM"
notifier by default every 300 seconds. This can be changed with the NOCOMMWARNTIME set-
upsmon usually gives up root powers for the process that does most of the work, including
handling signals like SIGHUP to reload the configuration file. This means your
upsmon.conf(8) file must be readable by the non-root account that upsmon switches to.
If you want reloads to work, upsmon must run as some user that has permissions to read the
configuration file. I recommend making a new user just for this purpose, as making the
file readable by "nobody" (the default user) would be a bad idea.
See the RUN_AS_USER section in upsmon.conf(8) for more on this topic.
Additionally, you can't change the SHUTDOWNCMD or POWERDOWNFLAG definitions with a reload
due to the split-process model. If you change those values, you must stop upsmon and
start it back up. upsmon will warn you in the syslog if you make changes to either of
those values during a reload.
SIMULATING POWER FAILURES
To test a synchronized shutdown without pulling the plug on your UPS(es), you need only
set the forced shutdown (FSD) flag on them. You can do this by calling upsmon again to
set the flag - i.e.:
upsmon -c fsd
After that, the master and the slaves will do their usual shutdown sequence as if the bat-
tery had gone critical. This is much easier on your UPS equipment, and it beats crawling
under a desk to find the plug.
upsc(8), upscmd(8), upsrw(8), upsmon(8)
upsset.cgi(8), upsstats.cgi(8), upsimage.cgi(8)
The NUT (Network UPS Tools) home page: http://www.exploits.org/nut/
NUT mailing list archives and information: http://lists.exploits.org/
Tue Oct 15 2002 UPSMON(8)